The career goal of the applicant is to become a leading researcher in the area of language acquisition and specific language impairment (SLI). To that end, additional coursework is planned in the areas of advanced statistical and methodological techniques (e.g., longitudinal and clinical designs), advanced topics in linguistics (i.e., derivational morphology), and grantsmanship/research dissemination. In addition, the candidate will complete a research training plan. The long-term goal of the candidate's research is to understand the nature of SLI by investigating the interface between the lexicon and morphology. Children with SLI are particularly vulnerable to deficits in morphosyntax and have difficulty learning new words, especially verbs. What is unclear is how the lexicon and morphosyntax might interact during development. Specifically, it is unknown whether the quality of lexical representations impacts morphosyntax in typically developing children and children with SLI. An additional critical issue is to identify effective methods for increasing the rate of morpheme production in children with SLI. Few studies have considered how manipulating lexical characteristics of the verbs used to treat a specific morpheme impacts clinical gains in morpheme production. The goal of Study 1 is to determine whether a lexical characteristic, namely neighborhood density (i.e., the number of words that are phonologically similar to a given word) influences morpheme production (i.e., third person singular) by typically developing children and children with SLI in sentence imitation and spontaneous elicitation tasks. The goal of Study 2 is to determine whether manipulation of the neighborhood density of treated verbs is a viable method for increasing gains in morpheme production (i.e., third person singular) for treated and untreated verbs by typically developing children and children with SLI. The resulting findings will determine the extent to which the lexicon influences morpheme production as well as gains in morpheme production in clinical treatment. The public health benefit of this research is that language deficits in children with SLI are well documented but little is known about how to effectively plan intervention to maximize gains with little attention being paid to lexical characteristics of treated verbs. Identifying clinical methods that maximize gains in treatment may prevent or minimize future academic failure.